/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root==NULL)
            return NULL;
        if( p->val < root->val && q->val < root->val )
            return lowestCommonAncestor( root->left, p, q );
        if( p->val > root->val && q->val > root->val )
            return lowestCommonAncestor( root->right, p, q );
        return root;
    }
};
